1. Field of the Invention
This invention relates generally to flexible link power transmission drives associated with internal combustion engine camshafts and accessories and the mounting therefor. More particularly, this invention relates to the integration of these flexible link drives to facilitate improved space efficiency and improved engine assembly. Specifically, this invention relates to integrating the flexible link power transmission drives and accessories associated with automotive internal combustion engines into a unit separable from an associated engine and a method for its use.
2. Description of the Prior Art
Internal combustion engines commonly require a portion of the mechanical power, available at their crankshafts, to be transmitted to devices not associated with primary purposes of the engines. Such primary purposes include providing the motive force for a vehicle or supplying power to be converted to electrical or hydraulic power in stationary applications. Some of these devices are commonly referred to as engine accessories or auxiliaries. Among these accessories are devices that perform functions necessary for the sustained operation of the engine. These include oil pumps to supply engine oil pressure, fuel pumps to pressurize the fuel supplied to carburetor or fuel injection systems, superchargers to increase manifold pressure, magnetos, generators or alternators to supply ignition spark, and water pumps to cause the circulation of coolant through engine cooling systems.
There are also accessories that perform functions not associated with either primary purposes of the engines or sustained operation of the engines. Examples of these include power steering pumps to pressurize power assisted steering units, generators or alternators to provide electrical power for vehicle electrical systems, not including ignition systems, vacuum pumps for the distribution of power to certain vehicle systems, and air conditioning compressors.
The crankshaft's mechanical power frequently must also be tapped to operate valves that control the flow of engine gases. Typically this includes the synchronous transmission of power from the crankshaft to one or more camshafts, which causes the valves to operate in a timed manner.
For all but the simplest of engines, either gear driven or flexible link driven power transmission systems have been used to power engine accessories and valve trains. Flexible link power transmission systems include those incorporating asynchronous power transmission belting, synchronous power transmission belting, and chain.
Gear driven systems, or gear trains, allow limited flexibility in the layout of the drive and in the geometrical relationships of the accessories, the camshafts, and the crankshafts, to each other. The gears must be held in strict relationship to each other, in terms of axial alignment and separation, and planar alignment. Also, there is a limited overall geometry available for varying the arrangement of power takeoff points in relation to the crankshaft. Gear trains also tend to generate excessive unwanted noise. Further, such gear trains generally require access to engine lubrication. However, gear trains can be capable of delivering substantial power over a wide range of rotational speeds. Accordingly, gear trains have found their greatest acceptance for use in large heavy-duty engine applications, especially of the compression ignition type, such as for large trucks.
Such a gear train generally requires multiple idler gears which must also be mounted on the engine, thereby further complicating the problem of providing proper support and drive to the valve train and engine accessories. Due to the rotational speed at which the engine valve trains and accessories must be driven and the rather high torque requirements of such valve trains and accessories, the individual gears making up the drive train must be of high precision. The performance capability of such high quality gearing may not be fully realized unless each gear making up the drive train is very carefully positioned to provide proper gear lash between the meshing gear teeth. Failure to achieve optimum gear lash can result in severe damage to the gear teeth requiring a costly and time-consuming overhaul of the gear train.
Attempts to accommodate the above noted limitations and requirements have spawned a variety of mounting approaches. For example, in some engines, the accessory drive gears are mounted directly on the engine cylinder block. However, mounting the gears directly on the cylinder block requires the machining of bores in the block to receive the shafts of the accessory and idler gears. Further, these bores must be precisely spaced relative to the crankshaft, the camshaft and each other. An error in machining even one bore could result in an unusable cylinder block, which must be discarded at considerable expense. Even when the bores are positioned correctly, separate alignment apparatus is required to achieve proper gear lash.
Another approach is to build a framework upon which to mount all of the gears of a gear train, including the crankshaft gear, the accessory gears, and the camshaft gear and to assemble all of these as a unit. The unit may then be mounted upon the cylinder block. This allows the assembly and maintenance of the gears in the strict relationships required and eliminates the need to precision machine bores directly in the cylinder block. Gear shaft receiving bores must still be positioned precisely on the framework. However, if a machining error is made only the framework is rendered unusable. The cost to the manufacturer of discarding an incorrectly bored framework is significantly less than the cost of discarding an incorrectly bored engine cylinder block.
Further, the piecemeal removal and replacement of accessories and their associated gears is highly impractical due to the gear train requirements described above. This has led to the mounting of certain accessories upon the framework. U.S. Pat. No. 1,647,434, to Chorlton describes such an arrangement.
Flexible link power transmission systems driving accessories and valve trains are not faced with these limitations and requirements. The need for precision placement of idler gears, drive gears, or accessories is greatly reduced. The accessories and camshafts can be placed over a substantially wider range of locations. The lack of gear train precision requirements makes piecemeal removal and replacement of accessories feasible. Also, flexible link transmissions, particularly those employing power transmission belting, tend to be quieter.
These qualities have led to flexible link power transmissions, to predominate in driving accessories and valve trains, in automotive engine applications. Currently, the most common set-up is for each accessory to be mounted upon separate mounting points or brackets, upon the engine cylinder block or cylinder head. Then, one or more asynchronous power transmission belts span from a crankshaft drive-wheel to each drive-wheel associated with each accessory. The drive-wheels associated with asynchronous power transmission belts are pulleys or sheaves. It is also common for tensioners to be mounted separately upon the cylinder blocks to provide tension upon the belts to facilitate proper operation of the power transmission drives.
Commonly, the camshafts are placed in the cylinder heads of the engines. A drive-wheel is attached to the camshaft. An additional flexible link then spans from a crankshaft drive-wheel to the camshaft drive-wheel. Due to the need for synchronous operation of the camshaft with the crankshaft, the flexible link will be either a synchronous power transmission belt or a chain. In either event, the drive-wheels for both the crankshaft and the camshaft are sprockets. As with the accessory drives, the camshaft drives also employee tensioners mounted directly upon the cylinder blocks or heads to tension the flexible links to facilitate proper operation of the drives. Generally, a flexible link camshaft drive is enshrouded by the cooperation of a front face of the engine and a front engine cover. This protects the drive from certain environmental influences, such as dirt, debris, and water.
A substitute for mounting each accessory upon separate brackets has been to include mounting points for accessories as part of the front cover. U.S. Pat. No. 5,692,466 to Hausmann et al. describes such an approach. This approach is stated to have the advantages that: 1) the accessory support brackets usually used can be omitted resulting in a reduction of cost and weight; 2) it provides mounting stiffniess resulting in good reaction force transmission to the accessories; 3) the resonance frequency of the camshaft drive cover is increased which greatly reduces vibration of the accessories and decreases engine noise during engine operation; and, 4) the cast structure for the front face of the engine cylinder block is simplified. Hausmann does not mention or suggest that the accessories can be first mounted upon the cover, followed by mounting the combination of the cover and accessories being mounted upon the cylinder block.
Yet another approach has been to provide a unitary mounting bracket for the engine accessories. Some portion of all accessories associated with any given engine are collected and mounted upon the bracket. The bracket and those accessories are then mounted as a unit upon the engine's cylinder block. The pulley for the crankshaft is mounted upon the crankshaft in a separate operation. Once these are completed, then the power transmission belt is installed about the pulleys. This approach apparently sought to derive the benefits of an improved assembly method whereby the number of steps necessary to the operation of a main assembly line were reduced and of a reduced inventory list.
However, none of these approaches individually, or in combination, have realized the full benefits available to a highly integrated flexible link power transmission system, of the present invention. Those benefits include a further reduction in the number of main assembly line steps and an additional reduction of inventory parts. Importantly, the present invention provides the opportunity for improved control over the alignment of the drive-wheels, giving rise to improved noise and wear characteristics for the flexible link. This improved control also provides the opportunity to tighten dimensional tolerances and thus provide more compact drives. Synchronous drives require clean and, in the case of chain drives, well-lubricated environments to produce satisfactory results. The present invention provides the further benefit of allowing improved encapsulation of the synchronous portion of the drive, associated with the camshaft, and thereby reducing the intrusion of foreign matter and the leakage of lubricant.
All of these benefits are very desirable to the automotive manufacturers. They cut assembly costs. They allow the power plant to be smaller, which in turn allows a smaller engine compartment, which can be traded for more interior room for a given size automobile. The resulting noise and wear reduction leads to improved consumer perception of quality and acceptance, and reduced warranty returns.
Accordingly, there remains the need for a highly integrated flexible link power transmission system that incorporates an engine drive frame whereupon: all or substantially all accessories, including associated drive-wheels, are pre-assembled; all other drive-wheels are affixed in preparation for final mounting upon the engine; the accessory drive or drives are configured including placement of the flexible links upon the drive-wheels; the camshaft drive, whether separate from or part of the accessory drive, are configured including placement of the flexible link about the sprockets; and where improved environmental protection to the camshaft drive is provided.